Such a thin metal film-laminated strip may be fabricated by heating and pressing a rolled or electrolytic metal film (e.g., copper film), or the like on an adhesive-coated surface of a plastic strip (e.g., polyimide strip), thereby adhering the metal film to the plastic strip. Alternatively, such a thin metal film-laminated strip may be fabricated by applying a resin solution to a surface of a thin metal film (e.g. copper film), wherein the resin solution is prepared by solving a thermosetting resin with a proper organic solvent and then curing the thermosetting resin by heat simultaneously with vaporizing the solvent. With these methods, it is impossible to cope with high density wiring required in the semiconductor industrial due to difficulty in finely processing such a metal film in a width of not more than 10 μm because the thermal performance of the adhesive is inferior to that of the substrate (e.g., polymer strip), and the resultant metal film formed by the methods has a thickness of not less than 10 μm, which is too thick to be finely processed. In addition, the above-mentioned methods reveal vulnerability in terms of dimensional stability and flexibility of a final product. Recently, in order to overcome these problems, a metal for forming a conductor circuit (hereinafter, to be referred to as “circuit forming metal”) is directly deposited on a plastic strip through sputtering, or a metal layer different from the circuit forming metal is deposited on the plastic strip through sputtering prior to depositing the circuit forming metal, so that the metal layer is interposed between the circuit forming metal and the plastic strip.
When forming a thin film by sputtering, a target formed from a thin film forming material is located within a vacuum chamber, a substrate is located at a position corresponding to the target, and then argon is introduced into the vacuum chamber. The target is negatively charged, and plasma is formed within the vacuum chamber, thereby ionizing argon. In addition, argon ions hit the surface of the negatively charged target. As such, particles are scattered from the target by the energy applied by the argon ions hitting against the target, and are then deposited on the substrate.
Sputtering processes employed for forming a thin metal film include diode sputtering, bias sputtering, RF sputtering, triode sputtering, and magnetron sputtering. The magnetron sputtering, which is most frequently used among the above-mentioned sputtering methods, has an advantage in that because a magnet is mounted on the rear side of a target, plasma is formed more densely at the area corresponding to the magnet as compared to the other area, thereby rendering more atoms scattered from the target, which increases the deposition rate.
Even if a thin metal (e.g., copper) film is deposited through magnetron sputtering, the metal film is stressed if it has a thickness of several or more microns. Therefore, when forming a thick metal film with a thickness of several or more microns, a thickness of not more than 1 μM of the film is firstly deposited through a dry deposition process employing magnetron sputtering, and then the remainder of the film is formed through wet electroplating.
Like this, when forming a laminated film with a thickness of several or more microns, wet electroplating is also carried out in combination with a dry deposition process because it is difficult to control stress only with a dry deposition process. If wet electroplating is also employed, a process for manufacturing a flexible metal (e.g., copper) film-laminated strip is complicated, and a manufacturing space should be increased. As a result, manufacturing costs and time are substantially increased. Furthermore, the electroplating has a problem of causing environmental pollution.
However, if thin metal (e.g., copper) films to be laminated are formed completely through a dry deposition process, a metal film-laminated strip is liable to be deformed due to the stress induced in the laminated film as the thickness of the metal film is increased. Thus, it cannot be assured to obtain a thickness of several or more microns for the copper film-laminated strip.